diff --git a/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/controllers/Controller.cpp b/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/controllers/Controller.cpp
index 97a2b90..91f72fc 100644
--- a/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/controllers/Controller.cpp
+++ b/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/controllers/Controller.cpp
@@ -121,6 +121,15 @@ void Controller::removeComboPackage(const std::string& comboPackageID)
 {
 }
 
+/*
+Function: getInvoicesByUser
+Description: Retrieves all invoices associated with the currently authenticated user.
+             Converts them into a read-only map before returning.
+Parameters:
+    - None
+Returns:
+    - util::Map<std::string, const Invoice*> containing the user’s invoices
+*/
 util::Map<std::string, const Invoice*> Controller::getInvoicesByUser()
 {
     User* currentUser = m_authenticationManagementService.getAuthenticatedUser();
@@ -134,6 +143,15 @@ util::Map<std::string, const Invoice*> Controller::getInvoicesByUser()
     return userInvoicesReadOnly;
 }
 
+/*
+Function: completePayment
+Description: Completes payment for a specific invoice using the given payment mode.
+Parameters:
+    - invoiceID: std::string, ID of the invoice to be paid
+    - paymentMode: util::PaymentMode, mode of payment (e.g., ONLINE, OFFLINE)
+Returns:
+    - void
+*/
 void Controller::completePayment(const std::string& invoiceID, util::PaymentMode paymentMode)
 {
     m_paymentManagementService.completePayment(invoiceID, paymentMode);
@@ -154,5 +172,4 @@ void Controller::configureNotifications(const std::string& userID, bool paymentN
 
 void Controller::runSystemChecks()
 {
-}
-
+}
\ No newline at end of file
diff --git a/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/services/PaymentManagementService.cpp b/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/services/PaymentManagementService.cpp
index 094e104..8b67c7d 100644
--- a/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/services/PaymentManagementService.cpp
+++ b/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/services/PaymentManagementService.cpp
@@ -9,6 +9,15 @@
 #include "JobCard.h"
 #include "Enums.h"
 
+/*
+Function: createInventoryItemsMap (static helper)
+Description: Builds a map of inventory items required for a given service and adds them to the booking’s inventory map.
+Parameters:
+	- completeInventoryItemMapOfBooking: util::Map<std::string, InventoryItem*>&, map to store inventory items for the booking
+	- currentService: const Service*, pointer to the current service
+Returns:
+	- void
+*/
 static void createInventoryItemsMap(util::Map<std::string, InventoryItem*>& completeInventoryItemMapOfBooking, const Service* currentService)
 {
 	auto& currentRequiredInventoryItems = currentService->getRequiredInventoryItems();
@@ -19,6 +28,18 @@ static void createInventoryItemsMap(util::Map<std::string, InventoryItem*>& comp
 	}
 }
 
+/*
+Function: generateInvoice
+Description: Generates an invoice for a completed service booking.
+			 Validates that all job cards are completed, calculates labor and parts cost, applies discount,
+			 and stores the invoice in the datastore.
+Parameters:
+	- booking: ServiceBooking*, pointer to the service booking
+Returns:
+	- void
+Throws:
+	- std::runtime_error if booking is null or job cards are incomplete
+*/
 void PaymentManagementService::generateInvoice(ServiceBooking* booking)
 {
 	if (!booking)
@@ -56,6 +77,14 @@ void PaymentManagementService::generateInvoice(ServiceBooking* booking)
 	currentInvoices.insert(invoice->getId(), invoice);
 }
 
+/*
+Function: getInvoices
+Description: Retrieves all invoices associated with a specific customer.
+Parameters:
+	- customerID: std::string, ID of the customer
+Returns:
+	- util::Map<std::string, Invoice*> containing the customer’s invoices
+*/
 util::Map<std::string, Invoice*> PaymentManagementService::getInvoices(const std::string& customerID)
 {
 	util::Map<std::string, Invoice*>& currentInvoices = m_dataStore.getInvoices();
@@ -71,6 +100,18 @@ util::Map<std::string, Invoice*> PaymentManagementService::getInvoices(const std
 	return currentUserInvoices;
 }
 
+/*
+Function: completePayment
+Description: Completes payment for a specific invoice. Updates payment method, date, and status,
+			 then sends a notification to the customer.
+Parameters:
+	- invoiceID: std::string, ID of the invoice
+	- paymentMode: util::PaymentMode, mode of payment (e.g., ONLINE, OFFLINE)
+Returns:
+	- void
+Throws:
+	- std::runtime_error if the invoice ID is invalid
+*/
 void PaymentManagementService::completePayment(const std::string& invoiceID, util::PaymentMode paymentMode)
 {
 	auto& currentInvoices = m_dataStore.getInvoices();
diff --git a/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/CustomerMenu.cpp b/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/CustomerMenu.cpp
index a9f4d21..9f1d696 100644
--- a/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/CustomerMenu.cpp
+++ b/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/CustomerMenu.cpp
@@ -64,6 +64,14 @@ void CustomerMenu::viewServiceHistory()
 {
 }
 
+/*
+Function: selectInvoiceFromUserForPayment (static helper)
+Description: Lists all pending invoices for the customer and allows selection by index.
+Parameters:
+    - currentInvoices: util::Map<std::string, const Invoice*>&, map of customer invoices
+Returns:
+    - std::string: ID of the selected invoice, or empty string if none selected
+*/
 static std::string selectInvoiceFromUserForPayment(const util::Map<std::string, const Invoice*>& currentInvoices)
 {
     int currentIndex = 1, choice;
@@ -118,6 +126,14 @@ static std::string selectInvoiceFromUserForPayment(const util::Map<std::string,
     }
 }
 
+/*
+Function: selectPaymentMode (static helper)
+Description: Allows the customer to select a payment mode (ONLINE or OFFLINE).
+Parameters:
+    - None
+Returns:
+    - util::PaymentMode: Selected payment mode
+*/
 static util::PaymentMode selectPaymentMode()
 {
     int choice;
@@ -140,6 +156,15 @@ static util::PaymentMode selectPaymentMode()
     }
 }
 
+/*
+Function: completePayments
+Description: Allows the customer to complete pending payments for invoices.
+             Validates invoice selection and payment mode before completing payment.
+Parameters:
+    - None
+Returns:
+    - void
+*/
 void CustomerMenu::completePayments()
 {
 	util::clear();
@@ -155,6 +180,17 @@ void CustomerMenu::completePayments()
     std::cout << "Payment completed successfully.\n";
 }
 
+/*
+Function: displayInvoices (static helper)
+Description: Displays detailed information for all invoices associated with the customer,
+             including booking details, technician, discount, total amount, payment status, and items used.
+Parameters:
+    - currentUserInvoices: util::Map<std::string, const Invoice*>, customer’s invoices
+Returns:
+    - void
+Throws:
+    - std::runtime_error if a null invoice is encountered
+*/
 static void displayInvoices(util::Map<std::string, const Invoice*> currentUserInvoices)
 {
 	if (currentUserInvoices.getSize() == 0)
@@ -206,6 +242,14 @@ static void displayInvoices(util::Map<std::string, const Invoice*> currentUserIn
 	}
 }
 
+/*
+Function: viewInvoices
+Description: Displays invoices associated with the customer by calling displayInvoices.
+Parameters:
+    - None
+Returns:
+    - void
+*/
 void CustomerMenu::viewInvoices()
 {
 	util::clear();